The present invention relates to a hard disk drive and recording method, and more particularly to a hard disk drive that degausses a write head and a recording method for use with such a hard disk drive.
Information read/write devices using various types of media such as optical disks and magnetic tapes are known in the art. Among them, hard disk drives (hereinafter referred to as HDDs) have become popular as storage devices for computers to such an extent that they are one type of the storage devices indispensable for today's computers. Further, not limited to computer systems, HDDs are expanding more and more in application because of its excellent characteristics. For example, HDDs are used for moving picture read/write devices, car navigation systems, and removable memories for use in digital cameras.
Each magnetic disk used in HDDs has a plurality of tracks formed concentrically and each track is divided into a plurality of sectors. Servo data and user data are stored in each of the sectors. A head element makes access to a desired sector in accordance with the servo data stored in a sector, whereby it is possible to effect write or read of data to or from the magnetic disk.
The head element section usually comprises a write head and a read head. The write head converts an electrical signal or current, which corresponds to the information to be written, into a magnetic field, and writes the information onto the magnetic disk. The write head comprises a magnetic pole piece and windings around the magnetic pole piece. The direction of a current flowing to the write head is changed to change the direction of the magnetic field to be generated. The direction of magnetic disk magnetization varies with the direction of the magnetic field. Consequently, data according to the direction of magnetization is recorded on the magnetic disk. A write current, which is necessary for a write, is determined in accordance with required magnetic field strength and the number of windings around the magnetic pole piece.
If, for instance, the current flowing to the write head is suddenly decreased at the end of a write, the write head is magnetized. When the write head is magnetized, written data may be erased. To prevent the write head from being magnetized, a technology disclosed, for instance, by Patent Document 1 (Japanese Patent Laid-open No. 9-7137) changes a current flowing to the write head to a sinusoidal current and gradually attenuates the amplitude of the current. Another technology disclosed, for instance, by Patent Document 2 (Japanese Patent Laid-open No. 7-311922) performs degaussing by supplying a current flowing to the write head in a waveform other than prescribed in Patent Document 1. These degaussing methods reverse the polarity of a current, that is, reverse the direction of a current flow, while attenuating the current flowing to the write head. These degaussing methods are particularly used for perpendicular magnetic recording.
To increase the write speed, the HDD ensures that a current waveform transition, which occurs when the direction of a write current changes, is provided with an overshoot as indicated in FIG. 6(b). In other words, the direction of a current changes when a change occurs in the data value to be written. When the direction of the current changes, the write current needs to quickly reverse its direction. However, such a direction reverse is delayed by an inductance component of the write head. Consequently, a current change waveform becomes dull. As such being the case, the write current is momentarily increased to provide an overshoot at the time when the direction of the current changes. Subsequently, a predefined level of write current flows. This makes it possible to reduce the rise time (reversal time) between the instant at which the current flowing to the write head reverses and the instant at which the predefined write current level is reached. As indicated in FIG. 6(a), a write current generation circuit 260 for a conventional HDD is provided with an overshoot generation circuit, which comprises a switch 264 and a current source 266 to overshoot the current flowing to a write head 250 when the current reverses. The overshoot generation circuit causes the current source 266 to generate an overshoot current, which corresponds, for instance, to a certain percent of the write current. When the current reverses, the switch 264 turns on so that a current, which is the sum of the write current flowing from a current source 265 and the overshoot current flowing from the current source 266, flows to the write head 250. The current flowing to the write head 250 is supplied from a preamplifier AE circuit (AE: arm electronics), which is mounted inside an enclosure for the HDD. The AE is driven by signals from a hard disk controller (HDC) and read/write channel (R/W channel), which are mounted on a circuit board for controlling the HDD.
In a conventional hard disk drive in which the current flowing to the write head overshoots at the time of reversal in order to reduce the rise time, however, problems occasionally occurred when degaussing was performed after a write. The problems will be described with reference to FIGS. 7 and 8. FIG. 7 is a block diagram illustrating the configuration of an AE in a conventional HDD. FIG. 8 is a timing diagram illustrating signal waveforms that are generated at the time of degaussing.
The configuration of the AE will now be described with reference to FIG. 7. The AE 200 comprises a write current generator 260 and a degauss waveform generator 270. The write current generator 260 generates a current that is to be supplied to a write head 250. The degauss waveform generator 270 generates an attenuation waveform that is suitable for degaussing. In accordance with a signal waveform supplied from the degauss waveform generator 270, the write current generator 260 supplies a current for degaussing to the write head. The write current generator 260 comprises transistors 261a, 261b, 262a, and 262b, switches 263 and 264, and current sources 265 and 266. The transistors 261a and 261b are referred to as transistors 261, whereas the transistors 262a and 262b are referred to as transistors 262.
A normal write period during which a normal write is performed relative to the magnetic disk will now be described. An R/W channel 221, which is mounted on a circuit board 220, enters write data (WED) 211 and 212 into the AE 200. WD 211 and 212 are transmitted as differential signals whose polarities are opposite to each other. Therefore, FIG. 7 shows two write data signal lines. If WD 211 and 212 are not transmitted as differential signals, one signal line will suffice. Write data 211 (+WD) is a signal that is a reversal of write data (−WD) 212. More specifically, when the +WD 211 is High, the −WD 212 is Low. When the +WD 211 is Low, the −WD 212 is High. The direction of the magnetization pattern to be written on the magnetic disk changes in accordance with WD 211 and 212.
Further, an HDC 222, which is mounted on the circuit board 220, enters a write control signal (write gate signal) 213 into the AE 200. The write control signal 213 indicates whether a write is to be performed on the magnetic disk. A write is performed in accordance with the write control signal 213. More specifically, it is defined that when the write control signal 213 is High, a current flows to the write head 250 for performing a write on the magnetic disk. If the write control signal is Low, no write is performed on the magnetic disk. While the write control signal 213 is High, a normal write process is performed. The period during which the write control signal 213 is High is regarded as a normal write period.
The +WD is input to (A) contact of a switch 231. The −WD is input to (A) contact of a switch 232. While the write control signal 213 is High, the switches 231 and 232 select (A) contact. When the switches 231 and 232 select (A) contact, WD 211 and WD 212 from the R/W channel 221 are input to “Base” terminals of the transistors 261 and 262. During a normal write period, therefore, the direction of a current that is generated by the write current generator 260 and flows to the write head changes in accordance with WD 211 and WD 212. In other words, when the +WD 211 is High, the transistor 261 turns on and the transistor 262 turns off. Meanwhile, when the −WD 212 is High, the transistor 261 turns off and the transistor 262 turns on. Thus, a change occurs in the direction of a current that is generated by the write current generator 260 and flows to the write head 250. The following explanation assumes that a “negative” polarity current flows from left to right within the write head 250 when the transistor 261 turns on with the transistor 262 turning off, and that a “positive” polarity current flows right to left within the write head 250 when the transistor 261 turns off with the transistor 262 turning on. The current flowing to the write head 250 is supplied from the current sources 265 and 266 via the switches 263 and 264, which are provided in the write current generator 260.
The current source 265 supplies a write current for performing a write on the magnetic disk. For explanation purposes, it is assumed that the write current is 50 mA. More specifically, data may be written onto the magnetic disk when a current of +50 mA or −50 mA flows to the write head. During the normal write period, the current I1 supplied from the current source 265 is fixed at 50 mA. On the other hand, the current source 266 supplies an overshoot current. In other words, the current from the current source 266 flows to the write head 250 only when a change occurs in the direction of the current flowing to the write head. The switch 263 is provided between the current source 265 and the write head 250. The switch 264 is provided between the current source 266 and the write head 250. The switch 263 controls the current supply from the current source 265. The switch 264 controls the current supply from the current source 266.
The switch 263, which is connected to the current source 265, is controlled in accordance with the write control signal 213. In reality, however, the switch 263 is controlled in accordance with a superimposed signal 247, which is generated when a superimposition circuit 240 superimposes a degauss enable signal 271 over the write control signal 213. This control operation will be described later. During the normal write period, the write control signal 213 is High so that the switch 263 is on. In this instance, the current source 265 supplies a current to the write head 250.
The switch 264, which is connected to the current source 266, is controlled in accordance with an output that is generated by a single shot (S/S) 241. During the normal write period, the switches 231 and 232 select (A) contact. Therefore, the +WD 211 and −WD 212 are input to the single shot (S/S) 241. The single shot (S/S) 241 detects a rise of the +WD 211 or −WD 212. The output of the single shot (S/S) 241 becomes a signal that exhibits a pulse when a change occurs in the direction of the current flowing to the write head 250. Therefore, the switch 264 turns on when WD 211 and WD 212 rise. In other words, when a change occurs in the direction of the current flowing to the write head, the switch 264 turns on and a current flows from the current source 266 to the write head 250. For explanation purposes, it is assumed that the current source 266 supplies 20% of the current supplied from the current source 265. During the normal write period, the current supplied from the current source 266 is 10 mA.
When the overshoot current source 266 is used as described above, it is possible to reduce the rise time between the instant at which the +WD/−WD data value changes and the instant at which a preselected write current of 50 mA is reached. During the normal write period, the write current attempts to flow in a reverse direction in order to reach a peak current of 60 mA when the polarity reverses. Therefore, the time required to reach a current of 50 mA is rendered shorter, and then an overshoot occurs so that a current of 60 mA is reached. However, a current of 50 mA is soon restored.
A degauss period during which degaussing is performed will now be described. The AE 200 incorporates the degauss waveform generator 270 in order to generate a degauss current waveform.
The write control signal 213 enters the degauss waveform generator 270. The degauss waveform generator 270 generates the degauss enable signal 271 in accordance with the write control signal 213. More specifically, the degauss enable signal 271 is output when the write control signal 213 turns off, that is, when the normal write period terminates, allowing a write process to be followed by a read process. The degauss enable signal 271 has a pulse waveform that is High during the time corresponding to the degauss period during which degaussing is performed. When the degauss enable signal 271 is High, a degaussing operation is performed. When the degauss enable signal 271 is Low, no degaussing operation is performed. The degauss enable signal 271 remains High for a certain period of time after the end of the normal write period, and then reverts to Low. When the degaussing operation starts, the R/W channel 221 stops supplying WD 211 and WE 212.
The degauss waveform generator 270 incorporates an oscillator clock or constant frequency generator. The oscillator clock or the like is used to generate degauss write data 272 and 273. Degauss write data 272 is referred to as the +DWD. Degauss write data 273 is referred to as the −DWD. Degauss write data 272 and 273 are referred to as the DWD. As shown in FIG. 8, DWD 272 and 273 are pulse waveforms having a predetermined frequency and a predetermined pulse width. As indicated in FIG. 8, these pulse waveforms appear during the degauss period only. The +DWD 272 is a reversal of the −DWD 273. More specifically, when the +DWD 272 is High, the degauss write data 273 is Low. When the +DWD 272 is Low, the degauss write data 273 is High. The +DWD and −DWD are half a cycle out of phase and equal in pulse width.
The +DWD 272 is input to a (B) contact of the switch 231. The degauss write data 273 is input to a (B) contact of the switch 232. During the degauss period, the switches 231 and 232 have a (B) contact. Therefore, DWD 272 and 273 are input to the “Base” terminals of the transistors 261 and 262, respectively. A change occurs in the direction of the current flowing to the write head 250 in accordance with DWD 272 and 273. When the +DWD 272 is High, the transistor 261 turns on so that a current flows from left to right within the write head 250. In other words, a “negative” sign write current flows to the write head 250. When the −DWD 273 is High, the transistor 262 turns on so that a current flows from right to left within the write head 250. In other words, a “positive” sign write current flows to the write head 250. In this manner, it is possible to change the direction of the current flowing to the write head during the degauss period. During the degauss period, the polarity of the current flowing to the write head 250 reverses at fixed time intervals.
The switches 231 and 232 change in accordance with the degauss enable signal 271. More specifically, when the degauss enable signal 271 goes High, a (A) contact is superseded by (B) contact. While the degauss enable signal 271 is High, the switches 231 and 232 select a (B) contact. When the degauss enable signal 271 goes Low, the switches 231 and 232 revert to (A) contact. The switches 231 and 232 are connected to a (A) contact while the write control signal 213 is High to represent a write period. The signal input to the base terminals of the transistors 261 and 262 in the write current generator 260 changes depending on whether the normal write period or degauss period prevails.
During the degauss period, the switch 263 is controlled in accordance with the degauss enable signal 271. When the degauss enable signal 271 is High, the switch 263 turns on. Therefore, the switch 263 is on during the degauss period. Consequently, the current supplied from the current source 265 constantly flows to the write head 250 during the degauss period as well.
The switch 263 turns on/off in accordance with the write control signal 213 and degauss enable signal 271. The state of the switch 263 changes in accordance with the superimposed signal 247, which is obtained when the superimposition circuit 240 superimposes the degauss enable signal 271 over the write control signal 213. The superimposed signal 247 is obtained by extending the write control signal 213 for the degauss period. When the superimposed signal 247 is High, that is, when the write control signal 213 or degauss enable signal 271 is High, the switch 263 is on. The switch 263 remains on during the time interval between the instant at which the normal write period begins and the instant at which the degauss period ends. This ensures that the current supplied from the current source 265 flows to the write head 250 during the normal write period and during the degauss period.
The state of the switch 264 changes in accordance with an output that is generated by the single shot (S/S) 241. During the degauss period, the switches 231 and 232 have a (B) contact so that DWD 272 and 273 enter the single shot (S/S) 241. The single shot (S/S) 241 detects a rise in DWD 272 and 273. In other words, the output of the single shot (S/S) 241 becomes a signal that exhibits a pulse when a change occurs in the direction of the current flowing to the write head 250. The +DWD 272 and −DWD 273 have the same pulse width. The +DWD 272 is a signal that is a reversal of the −DWD 273. Therefore, the output of the single shot (S/S) 241 is a pulse waveform that has two times the frequency of DWD 272/DWD 273 as indicated in FIG. 8. The switch 264 turns on when DWD 272 and DWD 273 rise. More specifically, when a change occurs in the direction of the current flowing to the write head 250, the switch 264 turns on so that a current flows from the current source 266 to the write head 250. The current source 266 supplies 20% of the current supplied from the current source 265.
As described above, the state of the switch 264 changes in accordance with the output of the single shot (S/S) 241. WD 211 and WD 212 or the +DWD 272 and −DWD 273 enter the single shot (S/S) 241. The signal input to the single shot (S/S) 241 changes depending on whether the switches 231 and 232 select a (A) contact or a (B) contact. More specifically, when the switch 231 has a (A) contact, WD 211 and WD 212 enter the single shot (S/S) 241. On the other hand, when the switch 231 has a (B) contact, the +DWD 272 and −DWD 273 enter the single shot (S/S) 241. In other words, the signals entering the single shot (S/S) 241 are the same as the signals entering the transistors 261 and 262. The single shot (S/S) 241 extracts a rise of the two input signals. The overshoot current flows when a change occurs in the direction of the current flowing to the write head. Therefore, the switch 264 turns on when the on/off states of the transistors 261 and 262 change. More specifically, the switch 264 turns on when the transistor 261 changes from the “on” state to the “off” state and the transistor 262 changes from the “off” state to the “on” state or vice versa. This ensures that the switch 264 turns on when a change occurs in the polarity of the current flowing from the current source 265 to the write head 250. Consequently, when the polarity of the current flowing to the write head 250 reverses, the current supplied from the current source 266 flows to the write head 250.
During the degauss period, the switch 263 remains on as is the case with the normal write period. The switch 263 is controlled by the superimposed signal 247. Therefore, the switch 263 remains on during the normal write period and degauss period. During the degauss period, the switch 264 temporarily turns on the moment a change occurs in the direction of the current flowing to the write head 250 as is the case with the normal write period. Consequently, the current supplied from the current source 266 and the current supplied from the current source 265 both flow to the write head 250. In other words, when the polarity of the current flowing to the write head 250 reverses during the degauss period, the switch 264 turns on so that the current supplied from the current source 266 flows to the write head 250.
The magnitudes of the currents supplied from the current sources 265 and 266 will now be described. As shown in FIG. 7, the degauss waveform generator 270 generates digital data (DAC values) 274 and 275, which are to be supplied to the current sources 265 and 266. For setting the currents for current sources 265 and 266, digital data (DAC values) 274 and 275 are subjected to digital-to-analog conversion and then delivered to the current sources 265 and 266. In accordance with digital data (DAC values) 274 and 275, the current sources 265 and 266 set the magnitudes of the currents to be supplied. More specifically, the current source 265 determines the magnitude of its supply current in accordance with digital data 274, whereas the current source 266 determines the magnitude of its supply current in accordance with digital data 275. The magnitude of the current supplied from the current source 265 increases with an increase in digital data 274, and the magnitude of the current supplied from the current source 266 increases with an increase in digital data 275. The current source 265 flows a necessary write current during the normal write period so that the write head 250 may perform a write. On the other hand, the current source 266 flows an overshoot current during the normal write period so as to reduce the time required for reversing the direction of the write current.
During the normal write period, digital data 274 and 275 usually remains constant. It means that the current supplied from the current sources 265 and 266 are constant during the normal write period. During the degauss period, however, digital data (DAC values) 274 and 275 gradually decrease from a level prevailing during the normal write period. In other words, digital data 274 is maximized during the normal write period and gradually decreased during the degauss period. Therefore, the current I1 supplied from the current source 265 is maximized during the normal write period and gradually decreased during the degauss period. Since the current I2 supplied from the current source 266 is 20% of the current supplied from the current source 265, digital data 275 is also maximized during the normal write period and gradually decreased during the degauss period. Therefore, the current I2 supplied from the current source 265 attenuates at the same rate as the current I1 supplied from the current source 265.
It is assumed that the write current is 50 mA as indicated in FIG. 8. During the normal write period, a maximum current of 60 mA (a write current of 50 mA plus an overshoot current of 10 mA) flows to the write head as a peak current. In other words, a current of 60 mA flows to the write head 250 when a change occurs in the polarity of the current flowing to the write head 250. The following explanation assumes that the current flowing to the write head decreases in steps of 5 mA from a write current level of 50 mA during the degauss period.
As indicated in FIG. 8, the current I1 supplied from the current source 265 decreases in steps of 5 mA from a level of 50 mA (decreases to 45 mA, 40 mA, and so on to 0 mA) during the degauss period. Digital data 274 is decreased so that the current decreases in steps of 5 mA when the +DWD or −DWD rises. In this instance, the polarity of the current reverses. In other words, the current decreases in steps of 5 mA each time a change occurs in the polarity of the current flowing to the write head 250. Therefore, the current flowing from the current source 265 to the write head 250 attenuates from 50 mA to 0 mA while changing the polarity (decreases from 50 mA to −45 mA, +40 mA, −35 mA, and so on to 0 mA).
During the degauss period, the current I2 supplied from the current source 266 also decreases in the same manner as described above. Setup is performed so that the current I2 supplied from the current source 266 is 20% of the current I1 supplied from the current source 265. Therefore, the current I2 supplied from the current source 266 gradually decreases in steps of 1 mA from 10 mA to 9 mA, 8 mA, and so on to 0 mA. Consequently, the current flowing from the current source 266 to the write head 250 attenuates while changing the polarity (decreases to −9 mA, +8 mA, −7 mA, and so on to 0 mA). At the beginning of the degauss period (before the initial rise of the +DWD or −DWD), the polarity of the current flowing from the current source 265 to the write head is not reversed. Since the write current is still not reversed, the switch 264 is off. Therefore, the current flowing from the current source 266 to the write head 250 is 0 mA. The total current generated by the write current generator 260 is 50 mA including the current flowing from the current source 265 to the write head 250. The overshoot current is added to the flowing current at the moment the polarity indicating the direction of the write current reverses. Thus, the switch 264 turns on. The current flowing to the write head 250 is increased by the amount of the overshoot current. Therefore, when the overshoot current is taken into account, the current flowing to the write head during the degauss period attenuates to 50 mA, −54 mA, 48 mA, −42 mA, and so on to 0 mA as shown in FIG. 8.